Jasper Sitwell

Thor

Sitwell was first introduced as a Level 7 agent of S.H.I.E.L.D. He plays a minor role in the questioning of Thor when he tries to retrieve his hammer.

The Consultant

Sitwell meets Agent Phil Coulson to discuss a problem concerning the Avengers Initiative. The higher ups in S.H.I.E.L.D. want Emil Blonsky aka The Abomination to be a part of the team. Both agents realize it is a bad idea and decide they need a patsy to ask General Ross. The patsy would hopefully infuriate Ross enough that retrieveing the Abomination would be impossible. Sitwell volunteers, but Coulson says no they need someone special.

They send Tony Stark and Stark plays the perfect patsy (this explains the after credits scene found in The Incredible Hulk).

Avengers

Sitwell is briefly seen on the Helicarrier during the Battle for New York.

Item 47

Sitwell is tasked with retrieveing some of the missing alien tech after the Battle for new York. He tracks down a couple using the tech to rob banks and recuits them into S.H.I.E.L.D.

Captain America: Winter Soldier

Jasper Sitwell was on board the Leumarian Star when Nick Fury sent pirates to take it over.

After Alexander Pierce interrogated Captain America, who refused to give information about Project Insight after Nick Fury's "death", Pierce branded him a fugitive, and Sitwell launched a Quinjet to take Captain America down, but it ended up working the other way around.

After finding out that S.H.I.E.L.D. was HYDRA and enlisting the help of Sam Wilson, the trio (Steve, Natasha, and Sam) found Sitwell and took him up to a rooftop. They tried interrogating him, but he refused to give information, so Romanoff kicked him off the building, where Wilson caught him using his Falcon wings. He finally told them that the Insight helicarriers were programmed to evaluate people's past to predict their future, and take them out millions at a time. Later, on the way to the Triskellion, intending to use his biometrics to shut down Project Insight, the trio was attacked by the Winter Soldier, who threw Sitwell in front of a truck, killing him.